(1) Field of the Invention
The present invention relates to a method and an apparatus for measuring ash content of food stuff based on absorbance values obtained by irradiating light on samples and a calibration curve determined in advance, and more particularly to a method and an apparatus for measuring the ash content by utilizing a state in which an organic ingredient such as flavonoid pigment, phytic acid, pectin is well coupled to inorganic ingredients which results in the ash content.
(2) Description of the Related Art
The ash content is defined as the residue after the removable of organic ingredients and water from food stuff and is considered to correspond to the total quantity of the inorganic ingredients of the food stuff. Conventionally, for analyzing the ash content, the food stuff is heated to, for example, 550.degree. C., and the sample is reduced to ashes to the extent that the organic ingredients and water are removed and carbon is not present whereby the total quantity of the residue is regarded as the ash contents. In carrying out the conventional method for measuring the ash content, a considerable time is consumed for the removable of the organic ingredients and water.
There has been a constant demand for an apparatus with which the measuring of the ash content can be carried out in a short time. In an attempt to meet such a demand, there has been proposed an apparatus for measuring the ash content in which the content value of ash, which is a specific ingredient of a sample, is measured in a short time based on the absorbance value which is obtained by irradiating solely the near infrared rays on the sample whose ash content value is unknown and on the calibration curve which is predetermined from the absorbance values obtained by irradiating the near infrared rays on the sample whose ash content value is known and from the known ash content value. For the measurement of ash content of, for example, food stuff, the ash content measuring apparatus available today has been improved by the correlation with the actual ash content nearly up to about .+-.0.03%, and such a measuring apparatus is being utilized for the measurement of ash content in a product such as wheat flour in which its quality is greatly influenced by the ash content. The ash content is utilized also in other food stuff, and the food industry is attaching importance to the ash content of food stuff in general.
Conventionally, in the case of the wheat flour, it has been the practice to obtain the calibration curve based on the correlation with respect to the ash content in the near infrared ray region. Also, the practice was that no attention was paid to the state in which the ash content concentrates at epidermis (surface layer portion) of a wheat grain and the calibration curve was obtained based directly on the ash content and a predetermined ingredient. Thus, the measuring precision was no higher than .+-.0.03%.
In a country like Japan where the content impurity for a product such as wheat flour is severely regulated, there is a need to improve measuring apparatuses for a still higher measuring precision. In Japan, the wheat flour is classified into small groups of classes and end uses according to the ash content. For example, the wheat flour with the ash content being below 0.34% is classified as a special class, that with the ash content being 0.34% to 0.44% as a first class, that with the ash contents being 0.44% to 0.56% as a second class, and that with the ash content being above 0.56% as a third class.
Thus, if there occurs a difference in the actual ash content value and the measured ash content value obtained by using a measuring apparatus, the ranking of the wheat flour may be changed, and this affects not only the price of the product but also greatly affects the credibility of the quality of the product. Therefore, if an ash content measuring apparatus whose measuring precision is low is used in the flour milling step, it is not possible to effectively control the ranks of the wheat flour. The measuring precision desirable in the flour milling step is in the order of .+-.0.01%. Under the existing state of art, the rank control still largely depends on the sharp senses of the operator gained through the experience.